Electronic devices, such as a dynamic random access memory (DRAM), a ferroelectric random access memory (FeRAM), and an RF circuit, include a capacitor which plays a role as a condenser, and the area occupied by the capacitor in a device also has been becoming narrower in accordance with a demand for the miniaturization or high integration of the device in recent years. The capacitor has a basic structure in which a dielectric layer is sandwiched between both electrodes of an upper electrode and a lower electrode, and the electrostatic capacitance of the capacitor is proportional to the relative permittivity of the dielectric layer and the surface areas of the electrodes, but is inversely proportional to the distance between both electrodes, that is, the thickness of the dielectric layer and the like. Since it is not possible to limit the thickness of the dielectric layer, in order to secure a high electrostatic capacitance in a limited occupied area, it is necessary to use a dielectric material having a higher relative permittivity than the dielectric layer.
Therefore, instead of low-permittivity materials of the related art for which SiO2, Si3N4, and the like were used, ferroelectric thin films formed of a perovskite-type oxide, such as barium titanate (BaTiO3), barium strontium titanate (hereinafter referred to as “BST”), lead titanate (hereinafter referred to as “PT”), lead zirconate titanate (hereinafter referred to as “PZT”) or lanthanum-added lead zirconate titanate formed by adding a small amount of lanthanum to PZT (hereinafter referred to as “PLZT”), are attracting attention. As a method of forming a ferroelectric thin film, chemical solution deposition (CSD), such as a sol-gel method, in addition to physical vapor deposition, such as a vacuum deposition method, a sputtering method or a laser ablation method, and chemical vapor deposition (CVD) has thus far been widely and generally used.
Particularly, compared to CVD, the sputtering method, and the like, the sol-gel method does not require a vacuum process so that the manufacturing costs are low, and there is an advantage that it is easy to form a film in a wide area on a substrate. Furthermore, when the composition of a solution material being used for formation of a ferroelectric thin film is changed, it is easy to obtain the composition of a film at a theoretical ratio, and an extremely thin ferroelectric thin film can be obtained, and therefore the sol-gel method is being expected as a method of forming a high-capacitance thin film capacitor and the like. In a manufacturing method using the sol-gel method, in general, first, a sol-gel solution is prepared, the prepared sol-gel solution is coated on a substrate, and firing and the like are carried out at predetermined temperatures, thereby obtaining a ferroelectric thin film. In a method of manufacturing a ferroelectric thin film using the sol-gel method, a spin coating method and the like have thus far been widely used to coat the sol-gel solution on a substrate. This is because, in a method of manufacturing a ferroelectric thin film using the sol-gel method, the spin coating method is excellent in terms of a possibility of increasing the film thickness uniformity in the substrate surface since a liquid is removed using, for example, a centrifugal force by rotating a substrate at a high speed.
However, in the spin coating method, there was a problem in that, when the sol-gel solution is coated on a substrate, since a majority of the material is scattered away from the substrate and thus wasted, the usage efficiency of the material is extremely poor. Therefore, studies are being made regarding manufacturing methods in which a method other than the spin coating method is used, and, as such a manufacturing method, for example, a method of manufacturing a ferroelectric thin film in which electrostatic spray deposition (hereinafter referred to as “ESD”) is used to spray the sol-gel solution on a substrate is known. The method of manufacturing a ferroelectric thin film using ESD is attracting attention particularly in terms of mass production properties or manufacturing costs since, when the sol-gel solution is coated on a substrate, it is possible to deposit approximately 90% of the sol-gel solution sprayed from a spout of a capillary on the substrate so that the usage efficiency of the material is extremely high and the film-forming speed is fast. Among the ESD, a method of manufacturing a high-density PZT ferroelectric thin film in which an electrostatic spray solution having, when the metallic compound-converted mass of a metallic compound dissolved in the sol-gel solution is represented by A and the mass of powder is represented by B, a ratio of B with respect to (A+B) of 83% is coated into 60 layers so as to form an approximately 28 μm-thick film, is disclosed (refer to Non Patent Document 1).